Surface-modified bioresorbable electrospun scaffolds for improving hemocompatibility of vascular grafts

Antibacterial nonwoven materials in medicine and healthcare

Bacterial infection has always been a severe challenge for mankind. The use of antibacterial nonwoven materials provides a lot of convenience in daily life and clinical practice grammar revision, it has become an important solution to avoid bacterial infection in clinical and daily life. This review systematically examines the spin bonding, melt blown, hydroneedling and electrospinning methods of nonwoven fabrication materials, and summarizes the antibacterial nonwoven materials fabrication methods. Finally, the review discusses the applications of antibacterial nonwoven materials for medical protection, external medical and healthcare, external circulation medical care implantable medical and healthcare and intelligent protection and detection. This comprehensive overview aims to provide valuable insights for the advancement of antibacterial nonwoven materials in the domain of medicine and health care. In the future, antibacterial nonwoven materials are expected to evolve towards biodegradability, composite materials, functionalization, minimally invasive techniques, diversification, and intelligence, thereby holding immense potential in healthcare.

Functional Efficacy of Tissue-Engineered Small-Diameter Nanofibrous Polyurethane Vascular Grafts Surface-Modified by Methacrylated Sulfated Alginate in the Rat Abdominal Aorta

Improved design to imitate natural vascular scaffolds is critical in vascular tissue engineering (VTE). Smooth muscle cells originating from surrounding tissues require larger pore sizes relative to those of endothelial progenitor cells found in the bloodstream. Furthermore, biofunctionalized scaffolds mimic the microenvironment, cellular function, and tissue morphogenesis. Here, we fabricated macroporous and nanofibrous polyurethane (PU) bilayer tissue-engineered vascular grafts (TEVGs) by a salt-leaching method to achieve high porosities up to 30 μm. These grafts have a low porosity on the luminal side and a high porosity on the abluminal side. To enhance their properties, we surface-modified the PU scaffolds using heparin-mimicking methacrylated sulfated alginate (PU-MSA). We then evaluated these tubular scaffolds for their anticoagulation effect, protein adsorption, and cell attachment in vitro. The results revealed that TEVGs modified with sulfated alginate (PU-MSA) exhibited better anticoagulation (25 ± 1 min) and higher VEGF protein adsorption (75 ± 5 ng/mL) compared to other scaffolds. Moving to in vivo testing, we examined the TEVGs in a rat model for either 1 or 5 months. Through ultrasonication and various histological analyses, we assessed the functionality and biocompatibility of the TEVGs. Notably, the PU-MSA scaffold created a microenvironment conducive to cell homing and regeneration in the field of VTE.

Enhancing cellular affinity for skin disorders: Electrospun polyurethane/collagen nanofiber mats coated with phytoceramides

Although the use of thermoplastic polyurethane (Tpu) nanofiber mats as wound dressings is of great interest due to their mechanical properties, they are hindered by their poor wettability and bioavailability. In this study, we aimed to improve the cellular affinity of Tpu nanofiber mats for skin disorders by incorporating extracted collagen (Col) from tendons and physically mixed with a layer of phytoceramides (Phyto) to produce TpuCol@X-Phyto mats in which the weight % of Phyto relatively to the weight of the solution was X = 0.5, 1.0, or 1.5 wt% via facile electrospinning approach. The collective observations strongly indicate the successful incorporation and retention of Phyto within the TpuCol architecture. An increase in the Phyto concentration decreased the water contact angle from 69.4° ± 3.47° to 57.9° ± 2.89°, demonstrating improvement in the hydrophilicity of Tpu and binary blend TpuCol nanofiber mats. The mechanical property of 1.0 wt% Phyto aligns with practical requirements owing to the presence of two hydroxyl groups and the amide linkage likely contributing to various hydrogen bonds, providing mechanical strength to the channel structure and a degree of rigidity essential for transmitting mechanical stress. The proliferation of human skin fibroblast (HSF) peaked significantly 100 % with TpuCol@X-Phyto mats coated for X =1.0 and 1.5 wt% of Phyto. Electrospun scaffolds with the highest Phyto content have shown the lowest degree of hemolysis, demonstrating the high level of compatibility between them and blood. The TpuCol@1.5Phyto mat also demonstrated higher efficacy in antibacterial and antioxidant activities, achieving a rate of DPPH radical scavenging of 83.3 % for this latter property. The most notable wound closure among all tested formulations was attributed to higher Phyto. Thus, the developed TpuCol@1.5Phyto nanofiber formula exhibited enhanced healing in an in vitro epidermal model.

Small diameter vascular grafts: progress on electrospinning matrix/stem cell blending approach

The exploration of the next-generation small diameter vascular grafts (SDVGs) will never stop until they possess high biocompatibility and patency comparable to autologous native blood vessels. Integrating biocompatible electrospinning (ES) matrices with highly bioactive stem cells (SCs) provides a rational and promising solution. ES is a simple, fast, flexible and universal technology to prepare extracellular matrix-like fibrous scaffolds in large scale, while SCs are valuable, multifunctional and favorable seed cells with special characteristics for the emerging field of cell therapy and regenerative medicine. Both ES matrices and SCs are advanced resources with medical application prospects, and the combination may share their advantages to drive the overcoming of the long-lasting hurdles in SDVG field. In this review, the advances on SDVGs based on ES matrices and SCs (including pluripotent SCs, multipotent SCs, and unipotent SCs) are sorted out, and current challenges and future prospects are discussed.

The Influence of Textile Structure Characteristics on the Performance of Artificial Blood Vessels

Cardiovascular disease is a major threat to human health worldwide, and vascular transplantation surgery is a treatment method for this disease. Often, autologous blood vessels cannot meet the needs of surgery. However, allogeneic blood vessels have limited availability or may cause rejection reactions. Therefore, the development of biocompatible artificial blood vessels is needed to solve the problem of donor shortage. Tubular fabrics prepared by textile structures have flexible compliance, which cannot be matched by other structural blood vessels. Therefore, biomedical artificial blood vessels have been widely studied in recent decades up to the present. This article focuses on reviewing four textile methods used, at present, in the manufacture of artificial blood vessels: knitting, weaving, braiding, and electrospinning. The article mainly introduces the particular effects of different structural characteristics possessed by various textile methods on the production of artificial blood vessels, such as compliance, mechanical properties, and pore size. It was concluded that woven blood vessels possess superior mechanical properties and dimensional stability, while the knitted fabrication method facilitates excellent compliance, elasticity, and porosity of blood vessels. Additionally, the study prominently showcases the ease of rebound and compression of braided tubes, as well as the significant biological benefits of electrospinning. Moreover, moderate porosity and good mechanical strength can be achieved by changing the original structural parameters; increasing the floating warp, enlarging the braiding angle, and reducing the fiber fineness and diameter can achieve greater compliance. Furthermore, physical, chemical, or biological methods can be used to further improve the biocompatibility, antibacterial, anti-inflammatory, and endothelialization of blood vessels, thereby improving their functionality. The aim is to provide some guidance for the further development of artificial blood vessels.

Composites of Bacillus megaterium H16 derived poly-3-hydroxybutyrate as a biomaterial for skin tissue engineering

Composite films of Bacillus megaterium H16 derived PHB with 1%Poly-L-lactic acid (PLLA), 1%Poly-ε-caprolactone (PCL), and 0.3 % graphene nanoplatelets (GNP) were produced by solvent cast method. The composite films were characterized by SEM, DSC-TGA, XRD, and ATR-FTIR. The ultrastructure of PHB and its composites depicted an irregular surface morphology with pores after the evaporation of chloroform. The GNPs were seen to be integrated inside the pores. The B. megaterium H16 derived-PHB and its composites demonstrated good biocompatibility which was evaluated in vitro on HaCaT and L929 cells by MTT assay. The cell viability was best for PHB followed by PHB/PLLA/PCL > PHB/PLLA/GNP > PHB/PLLA. PHB and its composites were highly hemocompatible as it resulted in <1 % hemolysis. The PHB/PLLA/PCL and PHB/PLLA/GNP composites can serve as ideal biomaterials for skin tissue engineering.

Chitosan Hydrogel as Tissue Engineering Scaffolds for Vascular Regeneration Applications

Chitosan hydrogels have a wide range of applications in tissue engineering scaffolds, mainly due to the advantages of their chemical and physical properties. This review focuses on the application of chitosan hydrogels in tissue engineering scaffolds for vascular regeneration. We have mainly introduced these following aspects: advantages and progress of chitosan hydrogels in vascular regeneration hydrogels and the modification of chitosan hydrogels to improve the application in vascular regeneration. Finally, this paper discusses the prospects of chitosan hydrogels for vascular regeneration.

Current Strategies for Engineered Vascular Grafts and Vascularized Tissue Engineering

Blood vessels not only transport oxygen and nutrients to each organ, but also play an important role in the regulation of tissue regeneration. Impaired or occluded vessels can result in ischemia, tissue necrosis, or even life-threatening events. Bioengineered vascular grafts have become a promising alternative treatment for damaged or occlusive vessels. Large-scale tubular grafts, which can match arteries, arterioles, and venules, as well as meso- and microscale vasculature to alleviate ischemia or prevascularized engineered tissues, have been developed. In this review, materials and techniques for engineering tubular scaffolds and vasculature at all levels are discussed. Examples of vascularized tissue engineering in bone, peripheral nerves, and the heart are also provided. Finally, the current challenges are discussed and the perspectives on future developments in biofunctional engineered vessels are delineated.

Design of Nanotechnological Carriers for Ocular Delivery of Mangiferin: Preformulation Study

(1) Background: Mangiferin (MGN) is a natural compound, showing anti-inflammatory and antioxidant activities for the potential treatment of eye diseases. The poor physicochemical features of MGN (low solubility and high instability) justify its nanoencapsulation into nanostructured lipid carriers (NLC) to improve its ocular bioavailability. (2) Methods: Firstly, MGN-NLC were prepared by the high shear homogenization coupled with the ultrasound (HSH−US) method. Finally, unloaded and MGN-loaded NLC were analyzed in terms of ocular tolerance. (3) Results: MGN-NLC showed good technological parameters suitable for ocular administration (particle size below 200 nm). The ORAC assay was performed to quantify the antioxidant activity of MGN, showing that the antioxidant activity of MGN-NLC (6494 ± 186 μM TE/g) was higher than that of the free compound (3521 ± 271 μM TE/g). This confirmed that the encapsulation of the drug was able to preserve and increase its activity. In ovo studies (HET-CAM) revealed that the formulation can be considered nonirritant. (4) Conclusions: Therefore, NLC systems are a promising approach for the ocular delivery of MGN.

Electrospun nanofiber scaffold for vascular tissue engineering

Due to the prevalence of cardiovascular diseases, there is a large need for small diameter vascular grafts that cannot be fulfilled using autologous vessels. Although medium to large diameter synthetic vessels are in use, no suitable small diameter vascular graft has been developed due to the unique dynamic environment that exists in small vessels. To achieve long term patency, a successful tissue engineered vascular graft would need to closely match the mechanical properties of native tissue, be non-thrombotic and non-immunogenic, and elicit the proper healing response and undergo remodeling to incorporate into the native vasculature. Electrospinning presents a promising approach to the development of a suitable tissue engineered vascular graft. This review provides a comprehensive overview of the different polymers, techniques, and functionalization approaches that have been used to develop an electrospun tissue engineered vascular graft.

Use of 3D Printing for the Development of Biodegradable Antiplatelet Materials for Cardiovascular Applications

Small-diameter synthetic vascular grafts are required for surgical bypass grafting when there is a lack of suitable autologous vessels due to different reasons, such as previous operations. Thrombosis is the main cause of failure of small-diameter synthetic vascular grafts when used for this revascularization technique. Therefore, the development of biodegradable vascular grafts capable of providing a localized and sustained antithrombotic drug release mark a major step forward in the fight against cardiovascular diseases, which are the leading cause of death globally. The present paper describes the use of an extrusion-based 3D printing technology for the production of biodegradable antiplatelet tubular grafts for cardiovascular applications. For this purpose, acetylsalicylic acid (ASA) was chosen as a model molecule due to its antiplatelet activity. Poly(caprolactone) and ASA were combined for the fabrication and characterization of ASA-loaded tubular grafts. Moreover, rifampicin (RIF) was added to the formulation containing the higher ASA loading, as a model molecule that can be used to prevent vascular prosthesis infections. The produced tubular grafts were fully characterized through multiple techniques and the last step was to evaluate their drug release, antiplatelet and antimicrobial activity and cytocompatibility. The results suggested that these materials were capable of providing a sustained ASA release for periods of up to 2 weeks. Tubular grafts containing 10% (w/w) of ASA showed lower platelet adhesion onto the surface than the blank and grafts containing 5% (w/w) of ASA. Moreover, tubular grafts scaffolds containing 1% (w/w) of RIF were capable of inhibiting the growth of Staphylococcus aureus. Finally, the evaluation of the cytocompatibility of the scaffold samples revealed that the incorporation of ASA or RIF into the composition did not compromise cell viability and proliferation at short incubation periods (24 h).

Hemolytic, Biocompatible, and Functional Effect of Cellularized Polycaprolactone-Hydrolyzed Collagen Electrospun Membranes for Possible Application as Vascular Implants

In search of bioactive vascular prostheses that exhibit greater biocompatibility through the combination of natural and synthetic polymers, tissue engineering from a biomimetic perspective has proposed the development of three-dimensional structures as therapeutic strategies in the field of cardiovascular medicine. Techniques such as electrospinning allow obtaining of scaffolds that emulate the microarchitecture of the extracellular matrix of native vessels; thus, this study aimed to evaluate the biological influence of microarchitecture on polycaprolactone (PCL) and hydrolyzed collagen (H-Col) electrospun scaffolds, which have a homogeneous (microscale) or heterogeneous (micro-nanoscale) fibrillar structure. The hemolytic, biocompatible, and functional effect of the scaffolds in interaction with an in vitro fibroblast model was determined, in view of its potential use for vascular implants. Scaffolds were characterized by scanning electron microscopy and atomic force microscopy, Fourier transform infrared spectroscopy, wettability, static permeability, tensile test, and degradation. In addition, direct and indirect 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays were used to identify the cell viability of fibroblasts, fluorescence assays were performed to establish morphological changes of the cell nuclei, and the hemolytic effect of the scaffolds was calculated. Results showed that ethanol-treated biocompositescaffolds exhibited mass losses lower than 6.65% and slow wettability and absorption, resulting from an increase in secondary structures that contribute to the crystalline phase of H-Col. The scaffolds demonstrated stable degradation in saline during the incubation period because of the availability of soluble structures in aqueous media, and the inclusion of H-Col increased the elastic properties of the scaffold. As regards hemocompatibility, the scaffolds had hemolysis levels lower than 1%; moreover, in terms of biocompatible characteristics, scaffolds exhibited good adhesion, proliferation, and cell viability and insignificant changes in the circularity of the cell nuclei. However, scaffolds with homogeneous fibers showed cell agglomerates after 48 h of interaction. By contrast, permeability decreased as the incubation period progressed, because of the cellularization of the three-dimensional structure. In conclusion, multiscale scaffolds could exhibit a suitable behavior as a bioactive small-diameter vascular implant.

Tissue Engineering for Mimics and Modulations of Immune Functions

In the field of regenerative medicine, advances in tissue engineering have surpassed the reconstruction of individual tissues or organs and begun to work towards engineering systemic factors such as immune objects and functions. The immune system plays a crucial role in protecting and regulating systemic functions in the human body. Engineered immune tissues and organs have shown potential in recovering dysfunctions and aplasia of the immune system and the evasion from immune-mediated inflammatory responses and rejection elicited by engineered implants from allogeneic or xenogeneic sources are also being pursued to facilitate clinical transplantation of tissue engineered grafts. Here, current progress in tissue engineering to mimic or modulate immune functions is reviewed and elaborated from two perspectives: 1) engineering of immune tissues and organs per se and 2) immune evasion of host immunoinflammatory rejection by tissue-engineered implants.

Glycosaminoglycans: From Vascular Physiology to Tissue Engineering Applications

Cardiovascular diseases represent the number one cause of death globally, with atherosclerosis a major contributor. Despite the clinical need for functional arterial substitutes, success has been limited to arterial replacements of large-caliber vessels (diameter > 6 mm), leaving the bulk of demand unmet. In this respect, one of the most challenging goals in tissue engineering is to design a "bioactive" resorbable scaffold, analogous to the natural extracellular matrix (ECM), able to guide the process of vascular tissue regeneration. Besides adequate mechanical properties to sustain the hemodynamic flow forces, scaffold's properties should include biocompatibility, controlled biodegradability with non-toxic products, low inflammatory/thrombotic potential, porosity, and a specific combination of molecular signals allowing vascular cells to attach, proliferate and synthesize their own ECM. Different fabrication methods, such as phase separation, self-assembly and electrospinning are currently used to obtain nanofibrous scaffolds with a well-organized architecture and mechanical properties suitable for vascular tissue regeneration. However, several studies have shown that naked scaffolds, although fabricated with biocompatible polymers, represent a poor substrate to be populated by vascular cells. In this respect, surface functionalization with bioactive natural molecules, such as collagen, elastin, fibrinogen, silk fibroin, alginate, chitosan, dextran, glycosaminoglycans (GAGs), and growth factors has proven to be effective. GAGs are complex anionic unbranched heteropolysaccharides that represent major structural and functional ECM components of connective tissues. GAGs are very heterogeneous in terms of type of repeating disaccharide unit, relative molecular mass, charge density, degree and pattern of sulfation, degree of epimerization and physicochemical properties. These molecules participate in a number of vascular events such as the regulation of vascular permeability, lipid metabolism, hemostasis, and thrombosis, but also interact with vascular cells, growth factors, and cytokines to modulate cell adhesion, migration, and proliferation. The primary goal of this review is to perform a critical analysis of the last twenty-years of literature in which GAGs have been used as molecular cues, able to guide the processes leading to correct endothelialization and neo-artery formation, as well as to provide readers with an overall picture of their potential as functional molecules for small-diameter vascular regeneration.

Evaluation of human umbilical vein endothelial cells growth onto heparin-modified electrospun vascular grafts

One of the main challenges of cardiovascular tissue engineering is the development of bioresorbable and compliant small-diameter vascular grafts (SDVG) for patients where autologous grafts are not an option. In this work, electrospun bilayered bioresorbable SDVG based on blends of poly(L-lactic acid) (PLLA) and segmented polyurethane (PHD) were prepared and evaluated. The inner layer of these SDVG was surface-modified with heparin, following a methodology involving PHD urethane functional groups. Heparin was selected as anticoagulant agent, and also due to its ability to promote human umbilical vein endothelial cells (HUVECs) growth and to inhibit smooth muscle cells over-proliferation, main cause of neointimal hyperplasia and restenosis. Immobilized heparin was quantified and changes in SDVG microstructure were investigated through SEM. Tensile properties of the heparin-functionalized SDVG resembled those of saphenous vein. Vascular grafts were seeded with HUVECs and cultured on a flow-perfusion bioreactor to analyze the effect of heparin on graft endothelization under simulated physiological-like conditions. The analysis of endothelial cells attachment and gene expression (Real-Time PCR) pointed out that the surface functionalization with heparin successfully promoted a stable and functional endothelial cell layer.

Patterned dextran ester films as a tailorable cell culture platform

The elucidation of cell-surface interactions and the development of model platforms to help uncover their underlying mechanisms remains vital to the design of effective biomaterials. To this end, dextran palmitates with varying degrees of substitution were synthesised with a multipurpose functionality: an ability to modulate surface energy through surface chemistry, and an ideal thermal behaviour for patterning. Herein, dextran palmitate films are produced by spin coating, and patterned by thermal nanoimprint lithography with nano-to-microscale topographies. These films of moderately hydrophobic polysaccharide esters with low nanoscale roughness performed as well as fibronectin coatings in the culture of bovine aortic endothelial cells. Upon patterning, they display distinct regions of roughness, restricting cell adhesion to the smoothest surfaces, while guiding multicellular arrangements in the patterned topographies. The development of biomaterial interfaces through topochemical fabrication such as this could prove useful in understanding protein and cell-surface interactions.

Vascular Tissue Engineering: Polymers and Methodologies for Small Caliber Vascular Grafts

Cardiovascular disease is the most common cause of death in the world. In severe cases, replacement or revascularization using vascular grafts are the treatment options. While several synthetic vascular grafts are clinically used with common approval for medium to large-caliber vessels, autologous vascular grafts are the only options clinically approved for small-caliber revascularizations. Autologous grafts have, however, some limitations in quantity and quality, and cause an invasiveness to patients when harvested. Therefore, the development of small-caliber synthetic vascular grafts (<5 mm) has been urged. Since small-caliber synthetic grafts made from the same materials as middle and large-caliber grafts have poor patency rates due to thrombus formation and intimal hyperplasia within the graft, newly innovative methodologies with vascular tissue engineering such as electrospinning, decellularization, lyophilization, and 3D printing, and novel polymers have been developed. This review article represents topics on the methodologies used in the development of scaffold-based vascular grafts and the polymers used in vitro and in vivo.

Covalent grafting of PEG and heparin improves biological performance of electrospun vascular grafts for carotid artery replacement

Rapid endothelialization of small-diameter vascular grafts remains a significant challenge in clinical practice. In addition, compliance mismatch causes intimal hyperplasia and finally leads to graft failure. To achieve compliance match and rapid endothelialization, we synthesized low-initial-modulus poly(ester-urethane)urea (PEUU) elastomer and prepared it into electrospun tubular grafts and then functionalized the grafts with poly(ethylene glycol) (PEG) and heparin via covalent grafting. The PEG- and heparin-functionalized PEUU (PEUU@PEG-Hep) graft had comparable mechanical properties with the native blood vessel. In vitro data demonstrated that the grafts are of good cytocompatibility and blood compatibility. Covalent grafting of PEG and heparin significantly promoted the adhesion, spreading, and proliferation of human umbilical vein endothelial cells (HUVECs) and upregulated the expression of vascular endothelial cell-related genes, as well as increased the capability of grafts in preventing platelet deposition. In vivo assessments indicated good biocompatibility of the PEUU@PEG-Hep graft as it did not induce severe immune responses. Replacement of resected carotid artery with the PEUU@PEG-Hep graft in a rabbit model showed that the graft was capable of rapid endothelialization, initiated vascular remodeling, and maintained patency. This study demonstrates the PEUU@PEG-Hep vascular graft with compliance match and efficacious antithrombosis might find opportunities for bioactive blood vessel substitutes.

Fabrication of multilayer tubular scaffolds with aligned nanofibers to guide the growth of endothelial cells

Aligned electrospun fibers used for the fabrication of tubular scaffolds possess the ability to regulate cellular alignment and relevant functional expression, with applications in tissue engineering. Despite significant progress in the fabrication of small-diameter vascular grafts (SDVGs) over the past decade, several challenges remain; one of the most problematic of these is the fabrication of aligned nanofibers for multilayer SDVGs. Furthermore, delamination between each layer is difficult to avoid during the fabrication of multilayer structures. This study introduces a new fabrication method for minute delamination four-layer tubular scaffolds (FLTSs) that consist of an interior layer with highly longitudinal aligned nanofibers, two middle layers composed of electrospun sloped and circumferentially aligned fibers, and an exterior layer comprising random fibers. These FLTSs are used to simulate the structures and functions of native blood vessels. Here, thermoplastic polyurethane (TPU)/polycaprolactone (PCL)/polyethylene glycol (PEG) were electrospun to fabricate FLTSs or tubular scaffolds with completely random fibers layer (RLTSs). The surface wettability of the TPU/PCL/PEG tubular scaffold was tested by water contact angle analysis. In particular, compared with RLTSs, FLTSs showed excellent mechanical properties, with higher circumferential and longitudinal tensile properties. Furthermore, the high viability of the human umbilical vein endothelial cells (HUVECs) on the FLTSs indicated the biocompatibility of the tubular scaffolds comparing to RLTSs. The aligned and random composite structure of the FLTSs are conducive to promoting the growth of HUVECs, and the cell adhesion and proliferation on these scaffolds was found to be superior to that on RLTSs. These results demonstrate that the fabricated FLTSs have the potential for application in vascular tissue regeneration and clinical arterial replacements.

Wavy small-diameter vascular graft made of eggshell membrane and thermoplastic polyurethane

In this study, a small-diameter, double-layered eggshell membrane/thermoplastic polyurethane (ESM/TPU) vascular graft with a wavy structure was developed. The avian eggshell membrane, a fibrous structure similar to the extracellular matrix (ECM), has the potential to yield rapid endothelialization in vitro. The dopamine and heparin modification of the ESM surface not only promoted human umbilical vein endothelial cell (HUVEC) proliferation via cytocompatibility assessment, but also improved its anticoagulation properties as verified in platelet adhesion tests. The biomimetic mechanical properties of the vascular graft were provided by the elastic TPU fibers via electrospinning using a wavy cross-section rotating collector. The advantage of combining these two materials is to make use of the bioactivity of ESM as the internal membrane and the tunable mechanical properties of TPU as the external layer. The circumferentially wavy structure of the vascular graft produced a toe region in the non-linear section of the stress-strain curve similar to that of natural blood vessels. The ESM/TPU graft's circumferential ultimate strength was 2.57 MPa, its strain was 339% mm/mm, and its toe region was found to be around 20% mm/mm. Cyclical tension tests showed that the vascular graft could maintain good mechanical properties and showed no structural damage under repeated extension tests.

Evolutionary approaches in protein engineering towards biomaterial construction

The tailoring of proteins for specific applications by evolutionary methods is a highly active area of research. Rational design and directed evolution are the two main strategies to reengineer proteins or create chimeric structures. Rational engineering is often limited by insufficient knowledge about proteins' structure-function relationships; directed evolution overcomes this restriction but poses challenges in the screening of candidates. A combination of these protein engineering approaches will allow us to create protein variants with a wide range of desired properties. Herein, we focus on the application of these approaches towards the generation of protein biomaterials that are known for biodegradability, biocompatibility and biofunctionality, from combinations of natural, synthetic, or engineered proteins and protein domains. Potential applications depend on the enhancement of biofunctional, mechanical, or other desired properties. Examples include scaffolds for tissue engineering, thermostable enzymes for industrial biocatalysis, and other therapeutic applications.

Regenerative and durable small-diameter graft as an arterial conduit

Despite significant research efforts, clinical practice for arterial bypass surgery has been stagnant, and engineered grafts continue to face postimplantation challenges. Here, we describe the development and application of a durable small-diameter vascular graft with tailored regenerative capacity. We fabricated small-diameter vascular grafts by electrospinning fibrin tubes and poly(ε-caprolactone) fibrous sheaths, which improved suture retention strength and enabled long-term survival. Using surface topography in a hollow fibrin microfiber tube, we enable immediate, controlled perfusion and formation of a confluent endothelium within 3-4 days in vitro with human endothelial colony-forming cells, but a stable endothelium is noticeable at 4 weeks in vivo. Implantation of acellular or endothelialized fibrin grafts with an external ultrathin poly(ε-caprolactone) sheath as an interposition graft in the abdominal aorta of a severe combined immunodeficient Beige mouse model supports normal blood flow and vessel patency for 24 weeks. Mechanical properties of the implanted grafts closely approximate the native abdominal aorta properties after just 1 week in vivo. Fibrin mediated cellular remodeling, stable tunica intima and media formation, and abundant matrix deposition with organized collagen layers and wavy elastin lamellae. Endothelialized grafts evidenced controlled healthy remodeling with delayed and reduced macrophage infiltration alongside neo vasa vasorum-like structure formation, reduced calcification, and accelerated tunica media formation. Our studies establish a small-diameter graft that is fabricated in less than 1 week, mediates neotissue formation and incorporation into the native tissue, and matches the native vessel size and mechanical properties, overcoming main challenges in arterial bypass surgery.

Adipose Stem Cell Translational Applications: From Bench-to-Bedside

During the last five years, there has been a significantly increasing interest in adult adipose stem cells (ASCs) as a suitable tool for translational medicine applications. The abundant and renewable source of ASCs and the relatively simple procedure for cell isolation are only some of the reasons for this success. Here, we document the advances in the biology and in the innovative biotechnological applications of ASCs. We discuss how the multipotential property boosts ASCs toward mesenchymal and non-mesenchymal differentiation cell lineages and how their character is maintained even if they are combined with gene delivery systems and/or biomaterials, both in vitro and in vivo.

Triple-Layer Vascular Grafts Fabricated by Combined E-Jet 3D Printing and Electrospinning

Small-diameter tissue-engineered vascular grafts are urgently needed for clinic arterial substitute. To simulate the structures and functions of natural blood vessels, we designed a novel triple-layer poly(ε-caprolactone) (PCL) fibrous vascular graft by combining E-jet 3D printing and electrospinning techniques. The resultant vascular graft consisted of an interior layer comprising 3D-printed highly aligned strong fibers, a middle layer made by electrospun densely fibers, and an exterior structure composed of mixed fibers fabricated by co-electrospraying. The biocompatible triple-layer graft was used for in vivo implantation, and results demonstrated that the longitudinally-aligned fibers within the lumen of the graft could enhance the proliferation and migration of endothelial cells, while maintained good mechanical properties. The exterior layer provided a pathway that encouraged cells to migrate into the scaffold after implantation. This experimental graft overcame the limitations of conventionally electrospun vascular grafts of inadequate porosity and lowly cell penetration. The unique structure of the triple-layer vascular graft promoted cell growth and infiltration in vivo, thus provided an encouraging substitute for in situ tissue engineering.

Oxygen-plasma treatment-induced surface engineering of biomimetic polyurethane nanofibrous scaffolds for gelatin-heparin immobilization

Polyurethane (PU) has been extensively used in vascular tissue engineering due to its outstanding mechanical performance and blood compatibility behavior. Here, biomimetic PU-based scaffolds were prepared using an electrospinning technique and gelatin-heparin was introduced as a surface modifier after oxygen plasma treatment to improve cell attachment and release an anticoagulation agent. Morphology, Fourier transform infrared (FTIR) spectroscopy, compression strength, swelling and biodegradation ratio, drug release level and cellular interactions were evaluated. According to the scanning electron microscopy (SEM) micrographs, gelatin-heparin immobilized PU nanofibers exhibited a smooth surface and a bead free structure that nanofibers distributed in the range of 300–1000 nm. The mechanical strength of constructs, swelling and biodegradation ratio, and drug release level illustrated higher values for oxygen plasma-treated samples compared with bilayered scaffolds. Cellular adhesion and biocompatibility ameliorated after plasma treatment. All the mentioned findings indicated the initial physicomechanical and biological potential of biomimetic PU-based fibers in the improvements of vascular scaffolds.

Electrospun vein grafts with high cell infiltration for vascular tissue engineering

Demand is increasing for functional small-diameter vascular grafts (diameter<6mm) for clinical arterial replacement. In the present study, we develop a bilayer poly(ε-caprolactone, PCL) fibrous vascular graft consisting of a thin internal layer made of longitudinally aligned fibers and a relatively thick highly porous external layer. The internal layer provides a scaffold with the necessary mechanical strength and enhances the growth of endothelial cells, whereas the external layer enhances cell motility through the scaffold bulk. The biocompatibility and biological performance of bilayer fibrous scaffolds are evaluated by in vivo experiments, molecular biology, and histology studies. Our bilayer scaffolds demonstrate much better fiber alignment and higher porosity than do normal electrospun vascular grafts with randomly distributed fibers. The results suggest that the proposed grafts can overcome limitations owing to the inadequate porosity, small pores, and poor cell infiltration of scaffolds fabricated by conventional electrospinning. The unique structure of bilayer scaffolds is satisfactory and promotes cell proliferation, collagen-fiber deposition, and ingrowth of smooth muscle cells and endothelial cells in vivo. The results of this study illustrate the strong potential of such bilayer fibrous scaffolds for vascular tissue engineering and regeneration.